Thermal cut-out and guard



Nov. 25, 1930. G. R. BROWN 19782359 THERMAL CUT-OUT AND GUARD Filed Aug. 29, 1927 Inventor. George R Brown His ttorneg.

Patented Nov. 25, 1930 UNITED STATES PATENT OFFICE GEORGE R. BROWN, 0F BRIDGEPORT, CONNECTICUT, ASSIGN OR TO-GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK THERMAL CUT-OUT AND GUARD Application led August 29, 1927. Serial No. 216,003. I

The present invention relates to electric distribution, and more especially to thermal safety devices for interrupting a circuit upon the occurrence of an excess of current 5 therein.

lThermal cut-outs ordinarily comprise a block or receptacle with terminals permanently intercalated in the circuit to -be protected and provided with contacts for engagement with' the detachable part or plug lcarrying the fusible element.

The object of my invention is the provision of an improved fuse plug and a guard which may be irremovably applied to an installed' block or receptacle of standard construction and serve to protect the contacts thereof from being .connected by other than a properly fused plug.

A common cause of accidents and injury to persons and things from electric currents is due to ignoranceor malicious nullication of the function of the safety cutout by short circuiting the terminals of the block or recceptacle by means of a metal disk or coin, and in consequence vof such practice there has arisen a wide-spread demand for means to guard againstv it.

One embodiment of my -invention is shown in the accompanying drawing, in which Fig. l is av vertical section of a standard cutout receptacle and of a guard and plug installed therein; Fig. 2 is an explodedview of the plug, and Fig. 3 is a similar view of the guard.

The standard recept-acle shown in the drawing comprises a porcelain base 1 having an integral annular wall 2 at the upper side, and in the well of which is a cylindrical contact in the form of a screw -shell 3 provided with a radial terminal 4 and binding screwr 5 for attachment of a line wire and an independent center contact 6 extending outwardly opposite to the terminal 4 and provided with a binding screw 7 for another wire.V

Either wire may be the supply circuit cenductor and the other the circuit to be protected by the cut-out.

The cut-out guard comprises a cup-shaped base 8 of insulation of a diameter to provide a slight annular space between the periphery of its iiange 9 and the inner surface of the screw-shell contact 3. A radial external shoulder 10 is provided near the base of the flange, while at the bottom of the base an annular rabbet 11 is formed and from which two notches 12 extend outwardly and upwardly to the periphery of the base. An axial bore 13 extends through the disk portion 14 and two diametrically disposed key recesses 15 are formed in the upper side of the disk portion 14.

A sheet steel locking ring 16 with diametrically disposed arms 17 bent upwardly at an angle therefrom and provided at their ends with backwardly directed teeth or spurs 18 is assembled in the rabbet 11 on the bottom of the base with the arms 17 projecting through the notches 12. A narrow screw shell 19 with two diametrically disposed holes 20 for the passage therethrough of the spurs 18 is secured to the base 8 by spinning its upper edge over the shoulder 10. A washer 21 of insulation is assembled beneath the shell 19 and a hollow rivet 22 is passed through the axial bore 13 of the base, the washer 21 and a metal ring 23, and then headed or spun outwardly over the latter, thereby ixedly securing all of the parts of the guard in assembled relation. The screw shell 19 is of a size easily to engage the inner surface of the receptacle screw shell 3 and the spurs 18 on account of the inclination of their arms 17 deflect inward during the screwing of the guard into the receptacle screw shell 3, but upon an attempt being made to back the guard outwardly they gouge into the metal of the receptacle screw shell 3 and positively lock the guard against removal.

The guard is turned home in the receptacle by means of a key or a Spanner wrench (not shown) inserted in the key recesses 15, so that the spun-over end of the hollow rivet 22 makes good Contact with the center contact 6 of the receptacle, while the head of the rivet provides a contact for engagement' by the plug when the latter is in place. It is to be noted that the arms 17 of the locking ring by engaging the side walls of the notches 12 prevent the ring from turning relative to the base 8, and that by their engaging with the sides of the holes 2O they prevent the screw shell 19 from turning relative to the base 8.

The plug comprises upper and lower cylindrical pieces of insulation 24 and 25. The upper piece 2l has a chamber 26 closed in by a metal cap 27 of ordinary construction and at the outside bottom endit is provided with a square projection 28. A metal screw shell 29, with an inturned flange 30 at its upper end has a square aperture 31 to fit over the projection 28 and an integral finger 32 bent upwardly therefrom and extending into the chamber 26 for attachment to one end of the fusible element 33 located therein, is secured to the underside of the upper plug part 24 by an insulating washer 34 having a square nole 35 fitting the projection 28 and clamped thereto by the lower plug part 25 which is also provided with a square recess 36 for the reception of the projection 28 and is fixedly bound to the upper plug part by a hollow rivet 37 extending axially upwardly through both plug parts 24 and 25 and headed or spun over at its upper end. The lower end of the fusible element 33 is secured in good Contact with the inner surface of the hollow rivet 37 by metal balls 38 forced therein.

The underside of the lower plug part 25 is recessed at 39 for the reception of the contact heads of the two hollow rivets 22 and 37 so that when the plug is screwed into the receptacle the space within the cup-shaped base 8 of the guard vis fully occupied by the lower plug part 25, while between the periphery of the latter and the plug screw shell 29 there is provided an annular channel for the telesco ic reception of the flange 9 of the guard ase.

It is to be noted that with the guard installed in the receptacle the crown iange 9 of the former serves as an insulating barrier adjacent the inner surface of the screw shell contact 3 of the latter and the well within the fiange is suiiiciently large to receive therein the lower part 25 of the plug which is of sufficient size to withstand the rough usage incident to ignorance or malicious attempts to short circuit the contacts by the interposition of coins or other pieces of metal between them.

While I have shown and described herein the best embodiment of the invention known to me, I do not desire to be restricted thereto.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A guard for cut-out receptacles having standard center and screw shell contacts, comprising a cup-shaped base of insulation, a center contact extending axially therethrough, and means on said base whereby it may be screwed into and fixedly held within the screw shell of said receptacle.

2. A guard for cut-out receptacles having standard center and screw-shell contacts, comprising a cup-shaped base of insulation,

a center contact extending axially therethrough, a thread on the periphery of said base to engage the said screw-shell contact of the receptacle, and locking spurs mounted on said cup-shaped base andadapted frictionally to engage said screw-shell of the receptacle upon screwing home said base therein.

3. A guardfor cut-out receptacles having standard center and screw-shell contacts, comprising a cup-shaped base of insulation, a center contact extending axially there,- through, a threaded shell secured to the periphery of said base and adapted to engage said screw-shell contact of the receptacle, and locking spurs projecting radially from said base and adapted to gouge into the metal of said screw-shell contact.

4. A guard for cut-out receptacles having center and screw-shell contacts, comprising a cup-shaped base of insulation having notches formed in the lower peripheral corner thereof, a sheet metal ring mounted on the bottom of said base and provided with bent arms disposed in said notches and having locking spurs at their outer ends, a threaded metal shell extending about the periphery of saidA base and provided with holes through which said bent arms project and an inturned vfiange mounted beneath said metal ring, an

insulating washer beneath said flange, and a center contact rivet extending through said base and said washer.

5. The combination with a cup-shaped guard of insulation for cut-out receptacles having standard center and screw-shell con-` tacts, of a fuse plug having an insulating base part adapted to lit within said cupshaped guard, and a screw-shell contact fixed to said plug in spaced relation to said base part and adapted to make engagement with the said screw-shell contact of the receptacle outside of said guard.

6. The combination of an upper plug base part provided with an internal chamber and a polygonal projection on the bottom thereof, a lower plug base part having in its top a recess corresponding to said polygonal projection, a screw-shell contact having an inturned fiange mounted on the bottom of the upper base part and provided with a polygonal hole through which said projection extends, an insulating washer mounted between said screw-shell ange and said lower base part, and a center contact rivet extending axially through said upper and lower base parts and serving to secure the several parts in fixed relation.

In witness whereof, I have hereunto set my hand this 25th day of August, 1927.

GEORGE R. BROWN. 

